The trend in modern fiber technology is toward the production of artificial yarns as uniform continuous filaments which are stronger than spun yarns. However, continuous filaments have a disadvantage for a number of applications; for example, in clothing, they lack bulk and have insufficient covering power. It is for this reason that processes for crimping or texturing continuous filaments, e.g., falsetwist texturing, the knit-deknit process, edge crimping, air jet treating, stuffer box bulking and chemical and/or thermal treatment, have been so extensively developed. Crimp is also introduced into rayon fibers by controlling the process of manufacture, for example, by adjusting the composition of the regenerating acid bath.
Therefore, in the manufacture of many types of textile yarns and fibers, the amount of crimp in a unit length of filament or fiber is of great importance and the measurement of crimp is a quality control test which is frequently used.
The usual procedure for counting the crimp in a filament or fiber is to place a representative sample alongside a length scale on a black velvet-covered board and then, with the aid of a magnifying glass, visually count the half-waves of crimp in a unit of scale length. The crimp count per unit length is normally considered one-half the count so obtained.
Disadvantages of the above method are the use of the human eye for very fine tedious work, as the crimp diameter may typically be only about 0.5 mm. to 1.5 mm., and rather poor reproducibility.